Tennis let calling system and method using ball flight characteristics

ABSTRACT

This disclosure relates to a let calling system and method, which is configured to determine that a let has occurred based on ball flight characteristics, as opposed to, for example, monitoring for changes in the net. In an example method, following a serve of a tennis ball, the method indicates that contact between the tennis ball and a tennis net has occurred when a flight characteristic of the tennis ball changes by a predetermined threshold amount in an area adjacent the tennis net.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.63/355,703, filed Jun. 27, 2022, the entirety of which is hereinincorporated by reference.

TECHNICAL FIELD

This disclosure relates to a let calling system and method, which usesball flight characteristics to determine whether a let has occurred, asopposed to, for example, monitoring for changes in the net.

BACKGROUND

On all tennis courts, perhaps the most notable part is the net. In oneknown example, a tennis net includes two main net posts placed at apre-determined height (e.g., 107 cm), and positioned a distance (e.g.,91.4 cm) outside the outermost (or doubles) sidelines of a tennis court.The net is typically composed of a woven or plastic netting supported byan upper net cable. The netting hangs from a strong metal cable via awhite net tape. The net cable is attached to one post and then to theopposite post, which has a crank that winds the cable so that the nettightens and rises up to the required height and a desired tension.

In the middle of the net, there is a center-strap (also known as amid-strap) which holds the net down by coming over the top of the netand being fastened to a clasp on the playing surface. This providesgreater tension than a crank could practically provide (by pulling downat the mid-point of the net), since cables generally will sag, andprovides the defined low part of the net in the center, and at andeterminable height, which is an important during play. The result is asemi-V shape running in the top part of the net, where the center strapprovides the regulation 91.4 cm height of the net in the middle. Due tothe weight of the net, the cable will have some degree of sag such thatthere will be an arc between the centerstrap and the net posts or singlesticks on either end.

A let is called in tennis only during a serve, which commences allpoints in tennis. A let is defined as a served ball (i.e., a ball struckduring a serve to start a point) making contact with the net as itpasses over and continues onwards, subsequently landing on the courtsurface within the “service box,” which are two delineated boxes definedby the painted lines on the court and the net itself. Tennis courts havebeen equipped with let detection systems, which are helpful indetermining when a let has occurred, as often lets are not readilyperceived by the players or tournament officials, given that the contactbetween the net and ball may be small and difficult to view with thehuman eye. Current let detection systems use sensors to detect themovement of the net caused by the force of the impact of the ball.

SUMMARY

In some aspects, the techniques described herein relate to a method,including: following a serve of a tennis ball, indicating that contactbetween the tennis ball and a tennis net has occurred when a flightcharacteristic of the tennis ball changes by a predetermined thresholdamount in an area adjacent the tennis net.

In some aspects, the techniques described herein relate to a method,wherein the flight characteristic is determined using a controller incommunicate with at least one of a camera, radar, infrared light, and alaunch monitor.

In some aspects, the techniques described herein relate to a method,wherein the flight characteristic is a spin rate.

In some aspects, the techniques described herein relate to a method,wherein the flight characteristic is one or more of spin rate,trajectory, velocity, and acceleration.

In some aspects, the techniques described herein relate to a method,wherein, following the serve of the tennis ball, the method includesindicating that contact between the tennis ball and the tennis net hasoccurred when at least two different flight characteristics of thetennis ball change by respective predetermined threshold amounts in thearea adjacent the tennis net.

In some aspects, the techniques described herein relate to a method,wherein, following the serve of the tennis ball, the method includesindicating that contact between the tennis ball and the tennis net hasoccurred when at least three different flight characteristics of thetennis ball change by respective predetermined threshold amounts in thearea adjacent the tennis net.

In some aspects, the techniques described herein relate to a method,wherein the area adjacent the tennis net includes a point on a sideopposite the side of the tennis net as a server of the tennis ball.

In some aspects, the techniques described herein relate to a method,wherein the area adjacent the tennis net includes a point on a same sideof the tennis net as a server of the tennis ball.

In some aspects, the techniques described herein relate to a method,wherein the area adjacent the tennis net includes a point above thetennis net.

In some aspects, the techniques described herein relate to a method,wherein the area adjacent the tennis net includes a point on a sideopposite the side of the tennis net as a server of the tennis ball, apoint on a same side of the tennis net as a server of the tennis ball,and a point above the tennis net.

In some aspects, the techniques described herein relate to a method,wherein the predetermined threshold amount is a drop of a predefinedpercentage.

In some aspects, the techniques described herein relate to a method,wherein the predetermined threshold amount is 5%.

In some aspects, the techniques described herein relate to a method,wherein the predetermined threshold amount excludes gradual changes inthe flight characteristic.

In some aspects, the techniques described herein relate to a method,wherein the predetermined threshold amount is a fingerprint and isrepresented as a sudden drop in the flight characteristic.

In some aspects, the techniques described herein relate to a system,including: a sensor configured to generate signals indicative of aflight characteristic of a tennis ball; and a controller configured tointerpret signals from the sensor and, based on the signals from thesensor, to indicate that contact between a tennis ball and a tennis nethas occurred when the flight characteristic of the tennis ball changesby a predetermined threshold amount in an area adjacent the tennis net.

In some aspects, the techniques described herein relate to a system,wherein the sensor is one of a plurality of sensors in communicationwith the controller.

In some aspects, the techniques described herein relate to a system,wherein each of the plurality of sensors is a different type of sensor.

In some aspects, the techniques described herein relate to a system,wherein the sensor is one of a camera, radar, infrared light, and alaunch monitor.

In some aspects, the techniques described herein relate to a system,wherein the flight characteristic is one or more of spin rate,trajectory, velocity, and acceleration.

In some aspects, the techniques described herein relate to a system,wherein the controller is configured to indicate that contact betweenthe tennis ball and the tennis net has occurred only if at least twodifferent flight characteristics of the tennis ball change by respectivepredetermined threshold amounts in the area adjacent the tennis net.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of the tennis ball in the instant before it makescontact with the net cord of a tennis net.

FIG. 2 is a view of the tennis ball in the instant after it makescontact with the net cord of a tennis net

DETAILED DESCRIPTION

The instant disclosure detects a let by monitoring for changes in theflight characteristics of the tennis ball, as opposed to monitoring forchanges in the net.

The velocity of the tennis ball has been measured in real time on tenniscourts for decades, for example, using the well-known IBM serve speedscreen.

FIG. 1 illustrates an example system of this disclosure. In FIG. 1 , atennis ball 1 (“ball 1”) is shown immediately above a tennis net 2 (“net2”), which is shown in cross-section. FIG. 1 represents the instant,such as a millisecond or so, prior to initial contact of the ball 1,which may be a served ball, with the net 2. The system includes at leastone sensor 3 configured to generate signals indicative of one or moreflight characteristics of the ball 1. The system may include one or moreof the sensors 3. The sensor 3 may be a camera, radar, infrared light,or a launch monitor, as examples. The sensor 3 may also be a LIDAR(Light Detection and Ranging) sensor or a sensor of a LIDAR system. Thesystem may include multiple sensors of the same type and mayalternatively or in addition include one or more sensors of differenttypes. This disclosure is not limited to any particular type ofsensor(s), so long as the sensor(s) is/are able to generate signalsindicative of one or more flight characteristics of the ball 1. Thesensor 3 includes or is in communication with a controller, which mayinclude one or more computing devices, configured to interpretinformation from the sensor 3 to determine various flightcharacteristics of the ball 1. In this disclosure, the sensor 3 is aimedat a top of the net 2. If other sensors are present, they may be aimedin other directions. The sensor 3 is configured to generate signalsindicative of flight characteristics of the ball 1 immediately beforethe ball 1 reaches the net 2 in the area adjacent the net, includingabove or at the net 2 (FIG. 1 ), and at an opposite side of the net 2(FIG. 2 ) after it has made contact with the net 2. In this way, thesystem (namely the controller) can determine whether any flightcharacteristic, such as spin rate, of the ball 1 has dropped by apredetermined threshold amount in the area adjacent the net 2 indicatingthat contact with the ball 1 and net 2 has occurred and a let should beindicated. A predetermined threshold known to correspond to contact withthe ball 1 and the net 2 is predefined and stored in the controller ofthe system. By defining a predetermined threshold amount, the systemreduces the likelihood that environmental factors such as wind gustswill cause the system to erroneously indicate contact between the ball 1and net 2 has occurred.

While spin rate is mentioned, the system could consider, alternativelyor additionally, other flight characteristics such as trajectory,velocity, acceleration (namely deceleration), etc. When those otherflight characteristics are considered, the controller is configured tocompare the change in those characteristics to other, respectivepredetermined threshold amounts to determine whether contact between theball 1 and the net 2 has occurred. The controller may be configured toconsider multiple characteristics simultaneously, and may only indicatethat contact has occurred if at least two of the monitoredcharacteristics meet or exceed the respective predetermined threshold.Alternatively, the system will indicate contact has occurred when onlyone characteristic meets or exceeds it corresponding predeterminedthreshold.

Tennis ball spin rates are currently detectable in modern technology,measuring from point of racket of the serving player to contact tobaseline on opposite side of the court by the receiving player. As theserve nearly always involves some degree of top spin, as opposed tobackspin by a ground stroke (“slice”) during a rally, which is theplaying of the point subsequent to the serve. The revolutions of theball can be tracked by using a fixed point on the ball, e.g. the printedlogo, or some other technique.

For the instant disclosure, flight characteristics of a served tennisball are monitored adjacent the tennis net. In this disclosure, a letwill be indicated if there is a sudden, relatively sharp, change in thespin rate, for example, at the specific point over or immediately afterthe tennis net (i.e., on a side opposite the side of the server). Thechange may be a drop of a predefined percentage, such as 5%, in the areaimmediately above or after the tennis net. This anomalous change ofrotation at the point the ball travels over the tennis net will indicatecontact with the net since the rotation of the ball will necessarily bedisrupted by this contact. The amount of change of spin and even theactual spin rate is irrelevant as all served tennis balls will havedifferent spin rates, depending on the skill of the player, wind, etc.As such, in this disclosure, it is the change in flight characteristicthat is monitored adjacent the net. Specifically, this disclosuremonitors for sudden changes in the flight characteristic to rule outgradual changes from wind gusts or steady deceleration of the tennisball over time. The sudden change monitored for in this disclosure maybe referred to as a fingerprint, and may be represented as a sudden dropin the flight characteristic by a predefined percentage in the areaadjacent the net. A graph over time would show a distinct drop in thespin rate at the millisecond the ball passes over the net. Because thisis a relative indication, the spin rate is ideally detected a specificduration (or distance) prior to the ball reaching the net, and thendetecting any telltale difference as it immediately then passes over thenet.

All tennis balls, regardless of the stroke (e.g. rally, volley, serve,etc.) will have various flight characteristics, including velocity,trajectory, and rotation. Rotation is of particular focus in one aspectof this disclosure, although velocity and trajectory, both separatelyand together with other flight characteristics, also come within thescope of this disclosure.

A tennis ball typically has a rotational speed of several thousandrotations per minute, depending upon the type of serve the playerchooses and if a first or second serve, the latter of which typicallyhave greater spin in lieu of the speed sought in a first serve in orderto have greater control to ensure it lands in the service box, and thusnot a “double fault.” Virtually all aces, defined as serves that thereceiver is unable to make contact with, are during the first serves.However, whether first or second serve, the ball will have a highrotation rate. This will typically be “top spin” where the rotation ofthe ball is in the direction of the forward path of the ball. Therotation is determined by the swing path, speed, and face angle of thetennis racket as it makes contact with the ball during a serve. The ballfrom a serve will have a trajectory of an arc from the contact pointtypically from a height of approximately 8 ft or more from the courtsurface at the base line, where serves occur, and maintaining a steadyangle moving towards the net as it travels from the baseline to passover the net, which traverses the width of the court with a height from91.4 cm in the middle to an incremental increase towards 100 cm as netheight increases closer to the single sticks or net posts, at 107 cm, ateither end.

The rotation rate of the ball is based upon the angle of impact of thetennis racket, the friction of the air (humidity, temperature, altitude,etc), the friction of the ball itself (having a “fuzz” covering itsentire surface), and other factors which may also be a constant, such asgravity. This rotation, often reaching 3,000 rpm (rotations per minute)or more will reach its peak almost immediately after leaving the tennisracket and incrementally decrease over time, until it comes in contactwith either the net or the court surface. This incremental reduction inrotation will be steady while also affected by the velocity which alsoincrementally decreases. The “top spin” rotation will affect the ballmore as the acceleration of the ball decreases, causing the ball toincrease its downward trajectory. The ball travelling at maximumvelocity will in turn affect the rotation of the ball but in apredictable steady manner. Similarly, the trajectory of the ball will beaffected by the rotation and gravity as the velocity decreases overtime.

In the instant disclosure, the measurement of up to three flightcharacteristics of the ball's travel towards and past the net, namelyvelocity, trajectory, and/or rotation, can be used to detect any impactof the ball upon the net. An impact by the ball of the net will changeall its flight characteristics relatively suddenly. The impact of thenet will necessarily reduce the velocity as the forward movement of theball will in some part be hindered by the net at contact. The trajectorywill change to varying amounts, by the contact with the net cord, whichwould necessarily interfere with the downward arc of the ball from thecontact of the racket from the exact point where the contact occurs. Thecharacteristics of velocity and trajectory can be relatively subtledepending on the degree to which the ball has contacted the net cord. Intennis, any contact of the ball with the net is deemed a “let” and theserve must be done again. The acceleration and trajectory may change toa very small degree, and can be largely masked by gusts of wind comingin any direction.

When considering, however, the rotation of the ball, a relatively freelyrotating ball will can exhibit a relatively greater and more perceptiblechange, at least to the system of this disclosure, upon impact with thenet. The rotation of the tennis ball will be disrupted when any objectimparts a force upon the ball. The net cord impacts a force upon theball which is deflected off its prior path, speed, and rotation, sincethe net cord does not absorb all of the ball's force, otherwise it wouldnot travel over the net to create a let. The impact with the net willhowever reduce the rpm and, in most cases, will cause the rpm tosuddenly drop in excess of a predefined threshold amount that isdetectable by the system of this disclosure.

Modern tennis technology can measure the rotation of all strokes intennis, such as forehand, backhand, serve, etc. The fact that thisdisclosure does not measure the ball after it strikes the court surfacemakes this analysis less complex, given that there are differentsurfaces in tennis, e.g. hard court, grass, clay, carpet, all of whichwill greatly affect the rotation and velocity (acceleration) of the ballupon court impact. In an aspect of this disclosure, the system detectsflight characteristics at the exact area over the net and then uses thatinformation to determine whether a sudden change, corresponding to apredefined threshold change that indicates contact with the net hasoccurred, has taken place by comparing the rpm of the ball apredetermined distance prior to the net (on the side of the server) andas it passes immediately over the net to an opposite side of the netfrom the server. In an aspect of this disclosure, a decrease in spinrate by an amount equal to or greater than the predetermined thresholdwill indicate contact with the net cord, hence indicate a let hasoccurred.

For example, as the RPM is steadily reducing over the approximate 12meters travel from the baseline, where the ball is set in motion, to thenet but at the point directly over the net cord has a sudden change,this fingerprint of change can be detected by an appropriate algorithm,and used to indicate contact has occurred (contact with the net beingthe only possible cause of such a fingerprint change in RPM). Such asystem is relatively more immune to the effects of wind on the net sinceit is motion of the ball that is being measured. While a strong gust ofwind can affect the trajectory or velocity of a serve, it has lesseffect on the rotation of the ball. In other words, while a head windwould necessarily affect the velocity of a ball, this would not be asudden event as two objects coming into contact with each other. Thus,by measuring the change at the relevant time, this let detection systemreliably determines whether an impact between a ball and net hasoccurred such that a let can or should be indicated. As the ball makesimpact with the net, the velocity of the ball results in the amount oftime the ball has contact with the net into a millisecond, or even lessif the ball barely clips the net cord. Rotation velocity exceeds thevelocity of the forward motion of the ball. However, the rotation of theball will be impeded when it comes into contact with the net, disruptingthe relatively free rotation of the ball (apart from air friction,gravity, etc). This disruption of the rate of rotation can be detectedby the resulting difference in rotation speed at the relevant time, i.e.when passing over the net.

It is also possible to mesh different metrics of the ball so as tocreate a broader picture of the ball as it travels over the net. Thedeceleration of the ball will increase due to impact with the net, andthe trajectory may change as well (although more difficult to track sucha small change due to the slightest contact of the ball.

It should be understood that directional terms are used in their normalmanner with reference to the game of tennis. Further, these terms havebeen used herein for purposes of explanation, and should not beconsidered otherwise limiting. Terms such as “generally,”“substantially,” and “about” are not intended to be boundaryless terms,and should be interpreted consistent with the way one skilled in the artwould interpret those terms.

Although the different examples have the specific components shown inthe illustrations, embodiments of this disclosure are not limited tothose particular combinations. It is possible to use some of thecomponents or features from one of the examples in combination withfeatures or components from another one of the examples. In addition,the various figures accompanying this disclosure are not necessarily toscale, and some features may be exaggerated or minimized to show certaindetails of a particular component or arrangement.

One of ordinary skill in this art would understand that theabove-described embodiments are exemplary and non-limiting. That is,modifications of this disclosure would come within the scope of theclaims. Accordingly, the following claims should be studied to determinetheir true scope and content.

1. A method, comprising: following a serve of a tennis ball, indicatingthat contact between the tennis ball and a tennis net has occurred whena flight characteristic of the tennis ball changes by a predeterminedthreshold amount in an area adjacent the tennis net.
 2. The method asrecited in claim 1, wherein the flight characteristic is determinedusing a controller in communicate with at least one of a camera, radar,infrared light, and a launch monitor.
 3. The method as recited in claim1, wherein the flight characteristic is a spin rate.
 4. The method asrecited in claim 1, wherein the flight characteristic is one or more ofspin rate, trajectory, velocity, and acceleration.
 5. The method asrecited in claim 4, wherein, following the serve of the tennis ball, themethod includes indicating that contact between the tennis ball and thetennis net has occurred when at least two different flightcharacteristics of the tennis ball change by respective predeterminedthreshold amounts in the area adjacent the tennis net.
 6. The method asrecited in claim 5, wherein, following the serve of the tennis ball, themethod includes indicating that contact between the tennis ball and thetennis net has occurred when at least three different flightcharacteristics of the tennis ball change by respective predeterminedthreshold amounts in the area adjacent the tennis net.
 7. The method asrecited in claim 1, wherein the area adjacent the tennis net includes apoint on a side opposite the side of the tennis net as a server of thetennis ball.
 8. The method as recited in claim 1, wherein the areaadjacent the tennis net includes a point on a same side of the tennisnet as a server of the tennis ball.
 9. The method as recited in claim 1,wherein the area adjacent the tennis net includes a point above thetennis net.
 10. The method as recited in claim 1, wherein the areaadjacent the tennis net includes a point on a side opposite the side ofthe tennis net as a server of the tennis ball, a point on a same side ofthe tennis net as a server of the tennis ball, and a point above thetennis net.
 11. The method as recited in claim 1, wherein thepredetermined threshold amount is a drop of a predefined percentage. 12.The method as recited in claim 11, wherein the predetermined thresholdamount is 5%.
 13. The method as recited in claim 1, wherein thepredetermined threshold amount excludes gradual changes in the flightcharacteristic.
 14. The method as recited in claim 1, wherein thepredetermined threshold amount is a fingerprint and is represented as asudden drop in the flight characteristic.
 15. A system, comprising: asensor configured to generate signals indicative of a flightcharacteristic of a tennis ball; and a controller configured tointerpret signals from the sensor and, based on the signals from thesensor, to indicate that contact between a tennis ball and a tennis nethas occurred when the flight characteristic of the tennis ball changesby a predetermined threshold amount in an area adjacent the tennis net.16. The system as recited in claim 15, wherein the sensor is one of aplurality of sensors in communication with the controller.
 17. Thesystem as recited in claim 16, wherein each of the plurality of sensorsis a different type of sensor.
 18. The system as recited in claim 15,wherein the sensor is one of a camera, radar, infrared light, and alaunch monitor.
 19. The system as recited in claim 15, wherein theflight characteristic is one or more of spin rate, trajectory, velocity,and acceleration.
 20. The system as recited in claim 19, wherein thecontroller is configured to indicate that contact between the tennisball and the tennis net has occurred only if at least two differentflight characteristics of the tennis ball change by respectivepredetermined threshold amounts in the area adjacent the tennis net.